While we have learned much about the flycatcher over this 10-year study, there are still many important areas for future research. These include: whether small populations have different population dynamics than the large populations we studied; development of improved or new demographic models to help guide complex management decisions; development of spatial models that link key determinants of flycatcher habitat (e.g., groundwater, stream flow) to the characteristics of suitable habitat (as identified by our models); development of decision tools to conduct scenario planning and address management issues; the role and impact that emerging disease threats may have on flycatcher populations; and a better understanding of the migration ecology of flycatchers. Coordination with Arizona Game and Fish DepartmentThroughout this research effort, project leaders and field staff of the USGS and AGFD worked cooperatively to collect the data upon which this report and other related science products are based. AGFD and USGS had concurrent field crews working within the same study sites at Roosevelt Lake and

Human transformation of aquatic systems and the introduction of nonnative species increasingly threaten the persistence of imperiled freshwater fishes. In response, large‐scale mechanical removal of nonnative fishes has been implemented throughout parts of the Colorado River basin to aid recovery of endangered fishes, but the effects of these efforts can be difficult to quantify. Fisheries population models for predicting outcomes of harvest regulations have been widely used to prevent overfishing of commercial and game stocks. Here, we used population models to investigate size‐specific removal efforts needed to overfish a nonnative population of Channel Catfish Ictalurus punctatus and thereby aid recovery of endangered fishes in the San Juan River, New Mexico and Utah. The minimum size of fish that were efficiently captured with electrofishing gear was 280 mm TL, and annual removal rates increased with fish size, ranging from 0.10 for 200‐mm fish to 0.44 for 600‐mm fish. Model results suggested that removal rates should be increased from 0.14 to a range of 0.21–0.34 to cause growth overfishing and should be increased to a range of 0.26–0.29 to cause recruitment overfishing at a minimum electrofishing size limit of 280 mm TL. However, model results indicated that overall population abundance and biomass are being substantially reduced compared to an unmanaged population. In concordance, long‐term monitoring data from 1991 to 2015 demonstrated a decrease in Channel Catfish TL and mass as well as an increase in catch rate variability since removal efforts intensified in 2006. Overall, current rates of removal will probably not achieve collapse of the nonnative Channel Catfish population in the San Juan River, but the reduction in size structure indicates that the population has responded to these efforts.

No abstract

Imperilment of native fishes worldwide, and particularly in the American Southwest, has prompted management actions to protect and recover threatened populations. Implementation of management activities, however, often proceeds without clear understandings of ecological interactions between native fishes and other biotic and physical components of the environment. Using data obtained in a 19-year, intensive monitoring effort across 288 km of the San Juan River in NM and UT, USA, we quantified relationships among large-bodied fishes and longitudinal environmental gradients, tested for faunal breaks of fishes and habitat structure along the river's course, and assessed the response of fishes to mechanical removal of non-native fishes and stocking of endangered fishes. Mesohabitat variation was not strongly linked to densities of large-bodied fishes, but we found strong and temporally consistent longitudinal patterns of native and non-native fishes: Native fish densities were highest upstream while non-native fish densities where highest downstream, potentially driven by differential responses to temperature regimes. Two breaks in the longitudinal structure of large-bodied fishes were identified and were associated with a man-made barrier and changes in the width of the river's floodplain. While densities of common native fishes were relatively constant during the study, non-native fish removal apparently reduced densities of one of two targeted species and densities of two endangered fishes increased as a result of stocking hatchery-reared fish. Results of this study suggest that large-bodied fishes of the San Juan River are responding to large-scale longitudinal gradients rather than small-scale habitat variation and management activities have altered densities of target species with limited responses by other fishes in the system.

Understanding patterns of animal distribution and abundance based on their movements is important to identify the habitats and factors that maximize growth and reproductive success. Despite stocking age-0 hatchery-reared Colorado Pikeminnow Ptychocheilus lucius for over 10 years in the San Juan River of Colorado, New Mexico, and Utah, the population consists primarily of stocked juveniles; adults remain rare. We investigated seasonal movement and growth of juvenile Colorado Pikeminnows in the San Juan River from 2009 to 2012 to inform recovery efforts throughout the Colorado River basin. Our results indicated fish made long-distance upstream movements from spring to summer while moving back downstream over winter. Seasonal movements may be associated with maximizing growth along longitudinal and seasonal temperature regimes. Length-at-age relationships reveal Colorado Pikeminnows in the San Juan River were larger than individuals of the same age in other populations in the upper Colorado River basin. While warmer water temperatures may have played some role in the larger lengths at age we observed, the hatchery-reared fish that are stocked at age 0 are probably larger than their wild-spawned counterparts of the same age. Variation in growth rates among size-classes indicates small Colorado Pikeminnows (<200 mm TL) had slower growth rates than larger individuals in the San Juan River, suggesting a possible resource limitation for smaller juvenile fish. Understanding how seasonal movement and growth of all life stages of Colorado Pikeminnow interact with modified river systems will be important for population conservation and recovery efforts in the upper Colorado River basin.